Hi,
On 2/9/22 17:01, Mika Westerberg wrote:
> Hi Hans,
>
> Thanks for looking into this!
>
> On Wed, Feb 09, 2022 at 04:12:32PM +0100, Hans de Goede wrote:
>> An alternative, much more elaborate fix would be to:
>>
>> 1. Add E820_TYPE_MMIO and E820_TYPE_MMIO_PCI_BRIDGE_WINDOW types to
>> enum e820_type and modify the 2 places which check for type == reserved
>> to treat these both as reserved too, so as to not have any functional
>> changes there
>>
>> 2. Modify the code building e820 tables from the EFI memmap to use
>> E820_TYPE_MMIO for MMIO EFI memmap entries and make e820_nomerge()
>> treat E820_TYPE_MMIO as non mergable to retain these as is
>>
>> 3. Modify pci_acpi_root_prepare_resources() to compare ACPI provided
>> bridge mmio windows against E820_TYPE_MMIO e820_Table entries and
>> if there is an exact match (as is the case on the Yoga C940)
>> then change the e820 type to E820_TYPE_MMIO_PCI_BRIDGE_WINDOW
>>
>> This means that we are now very narrowly treating EFI MMIO marked
>> regions special, in the special case where they are a 1:1 map
>> to an ACPI PCI bridge window resource.
>>
>> Note since we treat both E820_TYPE_MMIO and E820_TYPE_MMIO_PCI_BRIDGE_WINDOW
>> identical to the old RESERVED everywhere there is no functional change
>> here.
>>
>> 4. Modify arch/x86/kernel/resource.c: remove_e820_regions() to skip
>> e820 table entries with a type of E820_TYPE_MMIO_PCI_BRIDGE_WINDOW,
>> this would actually be a functional change and should fix the
>> issues we are trying to fix.
>>
>> Note an alternative would be to skip having the extra E820_TYPE_MMIO_PCI_BRIDGE_WINDOW
>> type and to skip step 3. above. That would boil down to doing the same
>> as your original patch in a somewhat cleaner manner.
>
> I agree and my vote goes for this last alternative (e.g skipping step 3).
> That would also make it slightly easier to follow the logic if someone
> in the future needs to investigate possible issues around this, I think.
As mentioned in my email from 10 seconds ago I think a better simpler
fix would be to just do:
diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
index 9b9fb7882c20..18656f823764 100644
--- a/arch/x86/kernel/resource.c
+++ b/arch/x86/kernel/resource.c
@@ -28,6 +28,10 @@ static void remove_e820_regions(struct resource *avail)
int i;
struct e820_entry *entry;
+ /* Only remove E820 reservations on classic BIOS boot */
+ if (efi_enabled(EFI_MEMMAP))
+ return;
+
for (i = 0; i < e820_table->nr_entries; i++) {
entry = &e820_table->entries[i];
I'm curious what you think of that?
Regards,
Hans
